Field of the Invention
The invention relates to a field effect-controlled, vertical semiconductor component. The field effect-controlled, vertical semiconductor component is disposed in a semiconductor element and has at least one internal zone of a first conductivity type, at least one basic zone of a second conductivity type which adjoins the internal zone and a first surface of the semiconductor element, and at least one source zone of the first conductivity type which is disposed in each basic zone.
Such field effect-controlled, vertical semiconductor components, which may be embodied as V-MOSFETs, D-MOSFETs, U-MOSFETs, are widely known and have been described in detail, for example, in a reference by B. Jayant Baliga, titled xe2x80x9cPower Semiconductor Devicesxe2x80x9d, PWS Publishing Company, pages 336 to 339.
In the off mode of such vertical semiconductor components, voltages may occur which are higher than the breakdown voltage of the semiconductor component. The drain/source off-state current which is caused by this causes, owing to the ohmic resistance in the basic zone, a voltage drop corresponding to the resistance in the basic zone. If the voltage drop exceeds the switch-off voltage of a parasitic diode at the pn junction between the basic zone and the drain zone, a parasitic bipolar transistor, whose emitter, base and collector are formed by the source zone, the basic zone and the drain zone, is undesirably switched on. The undesired switching on of the parasitic bipolar transistor is also referred to as a latch-up effect. In such a case, the off-state voltage of the semiconductor component drops significantly, i.e. by approximately 30% to 50%, which typically leads to the direct destruction of the semiconductor component itself. The latch-up effect is amplified by the fact that the voltage breakdown generally occurs at the edge of the basic zone, which is promoted by the curvature of the pn junction.
In order to improve the immunity to latching up, the resistance of the layer in the basic zone of the semiconductor component should therefore be as small as possible so that the voltage drop occurring here is as small as possible. However, the threshold voltage of the semiconductor component depends to a very high degree on the doping concentration in the basic zone, as a result of which tight limits are set on the reduction of the layer resistance in the basic zone.
If the doping concentration in the basic zone is nevertheless increased in order to reduce the layer resistance and thus improve the immunity to latching up, this additionally entails the risk of crystal fault formation which can be remedied only to a limited degree when a very high dose is used. In addition, when a very high implantation dose is used there is always also the risk of undesired defusing out of dopants into the semiconductor element. However, a semiconductor component in which the basic zones have, in view of all these measures, a very high doping concentration, with correspondingly off-state current densities in the basic zones will nevertheless latch in all cases.
Alternatively, it is possible that when the drain voltage is changed very rapidly a capacitive current flows which leads to a corresponding voltage drop in the basic zone, with the result that the parasitic bipolar transistor is switched on.
It is therefore necessary to ensure that in the off mode the parasitic bipolar transistor of the semiconductor component does not become active, i.e. is not latched, even when the off-state voltage rises above the breakdown voltage or when there is a rapid change in the drain voltage.
It is accordingly an object of the invention to provide a field effect-controlled, vertical semiconductor component that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the possibility of undesired switching on or off of a parasitic transistor is very largely excluded in the off mode.
With the foregoing and other objects in view there is provided, in accordance with the invention, a field effect-controlled, vertical semiconductor component disposed in a semiconductor element. The vertical semiconductor component contains at least one internal zone of a first conductivity type disposed in the semiconductor element, and the semiconductor element has a first surface and a second surface. At least one basic zone of a second conductivity type adjoins the internal zone and the first surface. At least one source zone of the first conductivity type is disposed in the basic zone. An intermediate zone of the first conductivity type is provided. At least one further basic zone of the second conductivity type is disposed in the semiconductor element, the intermediate zone is disposed between the further basic zone and the basic zone for spacing apart the further basic zone from the basic zone. At least one source contact zone connects the source zone, the basic zone and the further basic zone to one another with a low impedance.
Accordingly, a semiconductor component of the type mentioned at the beginning is provided which is characterized by at least one further basic zone of the second conductivity type which is spaced apart from the basic zone by an intermediate zone of the first conductivity type, and at least one source contact zone which connects the source zones, the basic zones and the further basic zones to one another with a low impedance.
The basic principle of the present invention consists in making available different basic zones that are spatially separated from one another. Here, the first basic zone is the actual current-conducting basic zone that is provided for forming the channel in the switched-on state. The further basic zone, which is typically disposed underneath the actual basic zone, is provided in the off mode for receiving an off-state voltage caused by an off-state current. In the off mode, a voltage drop caused by the off-state current occurs exclusively in the further basic zone. The voltage drop in the further basic zone does not, however, lead to charge carrier injection, and thus to switching on the parasitic bipolar transistor; a semiconductor component is thus advantageously made available without a latch-up effect.
A particular advantage of the invention lies, moreover, in the fact that the voltage drop in the further basic zone can be of any desired magnitude without the parasitic bipolar transistor switching on. The doping concentration in the basic zone can thus be adjusted in an optimum way to the setting of the threshold voltage of the semiconductor component; taking into account the immunity to latching up by a suitable selection of the doping concentration plays a small role here. A semiconductor component that advantageously provides greater degrees of freedom to manufacturing technology is thus provided.
The further basic zone is, as already mentioned, usually disposed under the actual basic zone and connected to the basic zone by a highly conductive source contact zone. It is particularly advantageous if the further basic zone is embodied as a layer buried in the internal zone. The highly doped, buried basic zone can typically be introduced into the internal zone by high-dose ion implantation.
In a particularly advantageous embodiment, the further basic zone is composed of two different regions that are disposed one underneath the other and are connected to one another. The two regions each have different penetration depths and different doping concentrations.
It is particularly advantageous if the first region has a high doping concentration and is disposed, with respect to the first surface, above the second region which has a much lower doping concentration. The first highly doped region thus takes up virtually the entire off-state current occurring in the further basic zone, and thus the voltage dropping there. The second region of the further basic zone that has a low doping level advantageously has a compensating effect for the doping in the drain region.
The second region of the further basic zone which has a low doping level takes up, to the benefit of the internal zone (=drain region) a significant proportion of the drain-source voltage, as a result of which the doping of the internal zone can be higher. Owing to the higher doping of the internal zone, the switch-on resistance can advantageously be significantly reduced with the same breakdown voltage, as a result of which the power drain of the current diverter component becomes correspondingly lower.
The further basic zones typically have a significantly higher doping concentration than the actual basic zones. However, it would also be advantageous if the further basic zones had the same doping concentration, or a lower doping concentration, than the actual basic zones. In this case, owing to the higher layer resistance, the vertical extent of the further basic zones can be significantly smaller, which results in the vertical extent of the JFET, and thus the resistance of this part of the semiconductor component, becoming smaller. In general, the further basic zone should be at least doped to such a level that it is not emptied when it is operated.
The basic zones and the further basic zones are electrically connected to one another by the formation of highly conductive, low-impedance contact. This is referred to below as a source contact zone and can be composed, according to a first exemplary embodiment, of very highly doped silicon of the same conductivity type as the base zone and the further base zone. The source contact zones are typically introduced in a trench shape into the semiconductor element from the front side of the wafer. It is particularly advantageous if the doping concentration of the source contact zone is significantly higher than the corresponding doping concentrations in the base zone and further base zone.
In a second exemplary embodiment, the source contact zone can also be embodied by a highly conductive metal stopper, which contains, for example, tungsten or an alloy containing tungsten.
In a third exemplary embodiment, the source contact zone can also be embodied by a silicide, for example platinum silicon (PtSi) which is applied to a trench wall and which is filled in with highly doped polysilicon.
A field effect-controlled semiconductor component according to the invention may be embodied as a vertical transistor structure, for example as a D-MOSFET, V-MOSFET, U-MOSFET etc. Such transistor structures are essentially a three-layered structure composed of the drain zone, the basic zone and the source zone. If the transistor structure is embodied as a power semiconductor component, an internal zone as a drift path, which has lower doping than the drain zone, is disposed between the basic zone and the drain zone. The source zone, the drain zone and, if appropriate, the internal zone have the same conductivity type, and the basic zone which is provided in order to form a channel zone by controlling the gate electrode has the opposite conductivity type.
Alternatively, the semiconductor component may also be embodied as a vertical insulated gate bipolar transistor (IGBT). In this case, an anode zone of the opposite conductivity type to that of the drain zone is provided between the drain zone and the rear metallization.
In the case of semiconductor components that are embodied as U-MOS""s or V-MOS""s, trenches are made in the semiconductor element in which the control electrodes are disposed. The trenches may be rectangular, U-shaped, V-shaped, trapezoidal etc. In the case of trench-shaped semiconductor components, the trenches extend from the front side of the wafer via the source zone, the basic zone, the intermediate zone, the further basic zone and into the internal zone of the semiconductor component. For structural reasons, two different channels are formed here by controlling the control electrode, i.e. a first channel is formed in the basic zone and a second channel is formed in the further basic zone. The particular advantage of such trench-shaped semiconductor components lies in the fact that the channels can be significantly shorter than in the case of lateral semiconductor components. The semiconductor components with a trench structure can thus be embodied with a significantly smaller pitch between two adjacent cells. This particularly advantageous exemplary embodiment thus provides not only improved immunity to latching up but also the advantage of a smaller pitch, which additionally improves the switch-on resistance.
In accordance with an added feature of the invention, a dielectric material is provided along with at least one control electrode adjoining the basic zone at the first surface and is spaced apart from the basic zone by the dielectric material. The basic zone generates at least one channel zone in a switched-on state when the control electrode is driven. At least one source electrode makes contact with the source contact zone at the first surface. A drain zone of the first conductivity type is disposed in the internal zone. At least one drain electrode makes contact over a large area with the drain zone.
In accordance with an additional feature of the invention, an anode region of the second conductivity type is disposed between the drain zone and the second surface.
In accordance with another feature of the invention, the semiconductor element has at least one trench formed therein, and has a control electrode disposed in the trench.
In accordance with a further feature of the invention, the trench extends from the first surface through the source zone, the basic zone, the intermediate zone, and the further basic zone, disposed in succession, as far as into the internal zone. It being possible to generate at least one further channel zone in the further basic zone by controlling the source contact zone.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a field effect-controlled, vertical semiconductor component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.